from __future__ import absolute_import

import inspect
import six
import sys

from sentry.utils.imports import import_string

PACKAGES = {
    'django.db.backends.postgresql_psycopg2': 'psycopg2.extensions',
    'sentry.db.postgres': 'psycopg2.extensions',
    'django.core.cache.backends.memcached.MemcachedCache': 'memcache',
    'django.core.cache.backends.memcached.PyLibMCCache': 'pylibmc'
}


def reraise_as(new_exception_or_type):
    """
    Obtained from https://github.com/dcramer/reraise/blob/master/src/reraise.py
    >>> try:
    >>>     do_something_crazy()
    >>> except Exception:
    >>>     reraise_as(UnhandledException)
    """
    __traceback_hide__ = True  # NOQA

    e_type, e_value, e_traceback = sys.exc_info()

    if inspect.isclass(new_exception_or_type):
        new_type = new_exception_or_type
        new_exception = new_exception_or_type()
    else:
        new_type = type(new_exception_or_type)
        new_exception = new_exception_or_type

    new_exception.__cause__ = e_value

    try:
        six.reraise(new_type, new_exception, e_traceback)
    finally:
        del e_traceback


def validate_settings(settings):
    for key, engine_key, engine_type in \
            [('DATABASES', 'ENGINE', 'database engine'), ('CACHES', 'BACKEND', 'caching backend')]:

        value = getattr(settings, key, {})
        for alias in value:
            engine = value[alias][engine_key]
            if engine not in PACKAGES:
                continue
            validate_dependency(settings, engine_type, engine, PACKAGES[engine])


def validate_dependency(settings, dependency_type, dependency, package):
    try:
        import_string(package)
    except ImportError:
        msg = ConfigurationError.get_error_message(
            "%s %s" % (dependency_type, dependency), package)
        reraise_as(ConfigurationError(msg))


class ConfigurationError(ValueError):
    """
    This error is thrown whenever a sentry configuration is wrong, or requires a third-party library
    that's not installed properly or can't be found.
    """

    @classmethod
    def get_error_message(cls, dependency, package):
        return """Python could not find %(package)s in your current environment (required by %(dependency)s). If you have it installed, maybe you are using the wrong python binary to run sentry?""" % {
            "dependency": dependency,
            "package": package
        }
